Field of the Invention
The present invention relates to a color filter substrate, a liquid crystal panel, and a repair method, in which a process utilizing laser light is performed.
Description of the Background Art
Recently, an FPD (Flat Panel Display) such as a liquid crystal panel has been utilized in many fields including a television set, a car navigation system, and a computer, because it is lightweight, thin in size, and has low power consumption. The panel of the FPD has been demanded to be large and to have no defective pixels year after year. Therefore, a repair technique for a defective part is inevitable for enhancing productivity in a manufacturing plant.
A liquid crystal panel includes a pair of opposing substrates. A distance between the pair of substrates of the liquid crystal panel is kept constant by a spacer. Liquid crystal is filled between the pair of substrates. One of the pair of substrates is an active matrix substrate (hereinafter also referred to as TFT (Thin Film Transistor) substrate) on which a thin-film transistor is formed. The other one (counter substrate) of the pair of substrates is a color filter substrate (hereinafter also referred to as CF).
A conductive film is formed on the TFT substrate and the CF. The drive of the liquid crystal is controlled by charges accumulated between the conductive film on the TFT substrate and the conductive film on the CF. The control of driving the liquid crystal on the portion where the transistor is formed and on a wiring portion on the TFT substrate is more difficult than the control of driving the liquid crystal on a display portion. In view of this, a shielding region (hereinafter also referred to as BM (Black Matrix)) is formed on the CF to suppress light transmission. With this structure, a clear image can be displayed.
The TFT substrate includes a plurality of independent pixels. When a pattern failure occurs, or an impurity (foreign matter) enters between the TFT substrate and the CF, on one pixel during a manufacturing process of the TFT, this pixel becomes a defective pixel as a bright spot brighter than the peripheral pixels. The defective pixel causes deterioration in quality of the liquid crystal panel. In the description below, the defective pixel as the bright spot is also referred to as a bright spot pixel.
A demand for a high-quality liquid crystal panel with no bright spot pixel has been more and more increasing in the market. Even if a liquid crystal panel has only one bright spot pixel out of several tens of thousands of pixels forming this liquid crystal panel, this liquid crystal panel is determined to be defective in some cases.
In order to solve the occurrence of the defect, a repair method (technique) is significant. The repair method includes a relatively easy method of repairing only one defective pixel out of several tens of thousands of pixels. According to this repair method, a yield and quality of the liquid crystal panel can be enhanced.
As the repair method of repairing the defective pixel that is a bright spot pixel brighter than peripheral pixels, a method of making the bright spot pixel into a black spot so as to make this bright spot pixel less noticeable than the peripheral pixels has been known. There has been proposed a method in which a gate terminal and a drain terminal of a target pixel are electrically connected by irradiation of laser light, and a constant voltage is applied to make the target pixel always display black, as a repair technique of making the bright spot pixel into a black spot.
This method is effective when a defective pattern is generated on the TFT substrate. However, this method cannot be used for a defect in which foreign matters are present between the TFT substrate and the CF. This method also entails a risk of reappearance of the bright spot pixel later due to disconnection between the portion irradiated with the laser light and the gate, when a connection between this portion and the gate is weak.
In addition to the method of making a bright spot pixel into a black spot with an electric control, there is a method of making a bright spot pixel into a black spot by blackening the bright spot pixel itself. For example, Japanese Patent Application Laid-Open No. 07-333588 (1995) describes a technique (hereinafter also referred to as a related technique A) of forming a light-shielding layer on a portion corresponding to a bright spot pixel (bright spot defect) on an outer surface of a glass substrate. This related technique A can make the bright spot pixel invisible from a front of the liquid crystal panel.
Japanese Translation of PCT International Application Publication No. 2010-530991 describes a technique (hereinafter also referred to as a related technique B) of blackening a part of a color material layer (color filter substrate), included in a CF, by irradiation of laser light to a portion (region) corresponding to a bright spot pixel. This related technique B can make the bright spot pixel unnoticeable.
However, the related technique B has a problem described below. Specifically, in the related technique B, high-output laser light for blackening the color material layer is focused on the color material layer, and with this state, this laser light is emitted to the color material layer. Therefore, the color material layer might be damaged. When the color material layer is damaged, a pigment component forming the color material layer flows into a liquid crystal layer, and the flown pigment component might cause a failure in an orientation film. When a failure occurs on the orientation film, quality of an image displayed on the liquid crystal panel is deteriorated.
Specifically, the related technique B has a problem in which a failure caused by damage of the color material layer is likely to occur, because high-output laser light for blackening the color material layer is focused on the color material layer, and with this state, this laser light is emitted to the color material layer. In order to prevent the occurrence of a failure caused by damage of the color material layer, the damage of the color material layer has to be prevented. The related technique A does not describe a technique of solving the problem of the related technique B.